Yeah, I'd say this is just a Catch.
Or an aspect
Let's say you do as Haru suggest: grind it up, mix it with oil and put it on your sword. Now you have a weapon that acts as a catch against anything that hates garlic - or, even if it's not a catch, it adds a bonus to attack(by tagging it) because the smell is distracting (I'm thinking vampires)
A necklace of garlic helps you to keep a vampire at bay (tagging for a bonus to dodge) or invoking for effect to keep the vampire from attacking at all.
So, weapon maneuvers, crafting maneuvers, scene aspects etc...
All things that can be tagged for effect or for bonuses.
Garlic as a declaration for a ward to protect a house against vampires would be a good one.
Edit: at most, if you were to liquefy it and put it in a water pistol and something was extremely allergic to it, I'd say weapon 0 . Normally water pistols don't hurt. But now it does, so it's infinitely more damaging now.